Merge pull request #85 from raytung/fix-readme-for-dockerv19-03-log

Added to README for supporting Docker v19.03

Author: okkez

README.md

@@ -168,13 +168,24 @@ Handle Docker logs splitted in several parts (using `partial_message`), and do n
 ```aconf
 <filter>
   @type concat
-  key message
+  key log
   partial_key partial_message
   partial_value true
   separator ""
 </filter>
 ```
 
+(Docker v19.03+) Handle Docker logs splitted in several parts (using `use_partial_metadata`), and do not add new line between parts.
+
+```aconf
+<filter>
+  @type concat
+  key log
+  use_partial_metadata true
+  separator ""
+</filter>
+```
+
 Handle Docker logs splitted in several parts (using newline detection), and do not add new line between parts (prior to Docker 18.06).
 
 ```aconf